1. Field of the Invention
The present invention relates to a cathode-ray tube apparatus (hereinafter referred to as "CRT") having a film stacked on the surface of a panel glass, and also relates to a method of producing the same.
2. Description of the Related Art
Recently, with the progress of computer simulation technology, it has become possible to make a practical strength analysis for CRTs, and large-sized CRTs and flat-panel CRTs, which are substantially equal to conventional CRTs in the bulb strength as being vacuum glass bulbs, have been realized by design according to the results of the strength analysis.
Such a large-sized or flat-panel CRT suffers, however, from some problems as stated below: To ensure the required bulb strength, the panel glass must be made thick in comparison to the conventional CRTs, and hence the overall weight of the CRT unavoidably increases. If the wall thickness of the panel glass is merely reduced to minimize the overall weight of the CRT, the bulb strength lowers, and the explosion-proof performance degrades.
Therefore, the existing CRTs employ a thin-walled panel glass and, at the same time, adopt an explosion-proof technique, e.g., banding, PPG laminating, resin bonding, and so forth.
Among the above-mentioned explosion-proof techniques, the banding method uses a panel glass which has been subjected to rough S/E polishing after pressing, followed by external polishing, which includes roughing, semi-finishing and finishing, and S/E polishing, thereby smoothing the surface thereof, and a band is fastened around the panel glass. The banding method includes the shrunk band method, the Kim chord method, and the T-band method, which are classified according to the manner in which the panel glass is banded. Among these methods, the shrunk band method is the mainstream of explosion-proof technique because it is suitable for mass-production. The PPG laminating method uses a panel glass which has been subjected to roughing and semi-finishing as external polishing but not subjected to finishing as external polishing, and it includes the steps of placing a spacer on the panel glass, placing a glass plate of 2 mm in thickness on the spacer, carrying out taping, injecting a thermosetting adhesive, and setting the adhesive by heating. The resin bonding method uses a panel glass which has been subjected to roughing, semi-finishing and finishing as external polishing, followed by S/E polishing, thereby smoothing the surface thereof, and a resin adhesive is coated on the panel glass to form a resin layer.
It should be noted that the conventional CRT manufacturing methods, including the above-described banding method, generally use a panel glass which has been subjected to rough S/E polishing after pressing, followed by external polishing, which includes roughing, semi-finishing and finishing, and S/E polishing. Such polishing is carried out so that irregularities of 5 um to 300 um in depth, which are produced on the outer surface of the panel glass as clamp marks of GOB or shrinkage marks during the pressing process, are reduced to 1 um or less, generally on the order of 0.1 um, to form a mirror surface, thereby preventing the fluorescent screen from undesirably glaring when the phosphors emit light.
As has been described above, various explosion-proof techniques have heretofore been carried out on large-sized or flat-panel CRTs in order to enable a reduction in the weight of the panel glasses thereof. To promote the achievement of a reduction in the overall weight of such CRTs, there has been a demand for a novel explosion-proof technique whereby the bulb strength is further enhanced.
The conventional CRTs use a panel glass which has been subjected to rough S/E polishing, followed by external polishing and S/E polishing, to prevent undesired glaring of the fluorescent screen. However, such polishing lowers the mechanical strength of the panel glass, and the polishing cost reaches 30% to 35% of the panel cost. Therefore, it has been demanded to make it possible to minimize polishing and increase the anti-explosion strength.
Among the conventional explosion-proof techniques, the PPG laminating method involves the problem that the taping and other processes are complicated, and a defective product is likely to occur because of bubbles which are generated during setting of the thermosetting adhesive by heating, although the finish polishing of the panel glass is omitted in this method. Further, it is difficult to prepare a thermosetting adhesive used in this method so that it has desired characteristics. As a result, undesired glaring of the fluorescent screen may occur. That is, the thermosetting adhesive used in the PPG laminating method is required to have a minimal change in volume before and after it becomes set upon heating because it is used to bond the panel glass and the glass plate stacked thereon. In addition, since the surface of the panel glass has been subjected to no finish polishing and is not a mirror surface, it is preferable that the refractive index of the thermosetting adhesive should be the same as that of the panel glass. However, if the thermosetting adhesive is prepared so that no substantial change in volume occurs, it is difficult to adjust the refractive index of the thermosetting adhesive so that the difference between the refractive indices of the thermosetting adhesive and the panel glass is not more than 1%. Consequently, undesired glaring of the fluorescent screen cannot effectively be prevented.